The invention relates to methods and compositions for the sustained release delivery of biologically active agents.
Polymeric materials have been widely used for manufacturing of medical devices, such as artificial organs, implants, medical devices, vascular prostheses, blood pumps, artificial kidney, heart valves, pacemaker lead wire insulation, intra-aortic balloon, artificial hearts, dialyzers and plasma separators, among others. The polymer used within a medical device must be biocompatible (e.g., must not produce toxic, allergic, inflammatory reactions, or other adverse reactions). It is the physical, chemical and biological processes at the interface, between the biological system and the synthetic materials used, which defines the short- and long-term potential applications of a particular device. In general, the exact profile of biocompatibility and biodegradation, including chemical and physical/mechanical properties i.e., elasticity, stress, ductility, toughness, time dependent deformation, strength, fatigue, hardness, wear resistance, and transparency for a biomaterial are extremely variable.
The polymeric coating of a medical device may also serve as a repository for delivery of a biologically active agent. Where the active agent is a pharmaceutical drug, it is often desirable to release the drug from the medical device over an extended period of time. Most systems for kinetically controlled direct drug delivery employ a polymer. For example, the agent may be released as the polymer enzymatically degrades or disintegrates in the body or may diffuse out of the polymeric matrix at a controlled rate. A site-specific drug transfer system can produce a high concentration of agent at the treatment site, while minimizing the adverse effects associated with systemic administration.
A polymeric system being used to control release of the drug must be free of impurities that trigger adverse biological responses (i.e., biologically inert), must produce the desired release profile, and must possess the mechanical properties required of the medical device.
In most cases biologically active agents are simply mixed with a polymer platform in a suitable solvent system. The biologically active agent is then released by particle dissolution or diffusion (when the non-bioerodable matrices are used) or during polymer breakdown (when a biodegradable polymer is used). In such systems the biologically active agents are released without regard to biological function or condition of the tissue at the site of implantation.
It is desirable to design a polymeric system which responds to a biological function or condition of the tissue at the site of implantation.